Since a liquid crystal display (LCD) device has characteristics of light weight, thinness and low power consumption, the LCD device has been widely used as a substitute for a display device of cathode-ray tube type. The LCD device includes first and second substrates that face each other. A liquid crystal layer is interposed between the first and second substrates. The LCD device uses optical anisotropy and polarization properties of liquid crystal molecules to display images. The LCD device includes a switching element, a pixel electrode, a common electrode, a color filter and so on. Particularly, the LCD device including a thin film transistor (TFT) as a switching element, referred to as an active matrix LCD (AM-LCD) device, has excellent characteristics of high resolution and displaying moving images.
Generally, the LCD device uses a glass plate as a substrate. However, since the glass plate is hard and has heavy weight, it is difficult for the glass plate to be used for fabricating a mobile instrument such as a mobile phone and a personal digital assistant (PDA). In addition, the substrate made of the glass plate is likely to break down by impacts.
To resolve the above problems, the LCD device using a flexible substrate is suggested. The flexible substrate is made of a transparent plastic plate, such as polyethylene phthalate, polyether sulfone, polyimide and so on, which has light weight and strength against impacts. The flexible substrate has a relatively lower transition temperature than the glass substrate, but the flexible substrate has advantages of lightness and flexibility. Unfortunately, the flexible substrate has several problems in the process of fabricating the LCD device. The flexible substrate waves during the process due to flexibility, and thus an adhesion-transferring method using a bonding agent fixing the flexible substrate to the glass plate is applied.
FIG. 1 is a schematic cross-sectional view of a flexible substrate after an adhesion-transferring method according to the related art. As shown in FIG. 1, in the adhesion-transferring method, the bonding agent is coated on the glass plate to form a bonding agent layer 30 and the flexible substrate 20 is disposed on the bonding agent layer 30. Accordingly, the glass plate 10, the bonding agent layer 30 and the flexible substrate 20 is sequentially laminated. Not shown in FIG. 1, the bonding agent layer 30 includes upper and lower layers. Because the bonding agent layer 30 should not be separate from the glass plate, the upper portion, which clings to the glass plate 10, has a strong adhesive strength than the lower portion. In contrast, the lower portion has a relatively weak adhesive strength to separate the flexible substrate from the bonding agent layer 30 after the fabricating process. The flexible substrate 20 is fixed to the glass plate 10, transferred into the fabrication process of the LCD device and fixed.
However, since the flexible substrate is fixed to the glass plate using double layers of the bonding agent, the fabricating process becomes complicated. Also, since bubbles are contained between the flexible substrate and the bonding agent layer, production yield decreases. Since the bonding agent layer has double-layered type, it is difficult to select the bonding agent.